Imagine a large rotor with an ID of 12". One normally uses an adjustable bore gage, or perhaps an inside rod micrometer, to check the diameter. But in this case, a hub in the center of the part presents an obstacle.

In the world of oil drilling there are some pretty big things. It's not just the rigs anchored out in the ocean that are huge; everything that goes along with them seems to get super-sized including the need for gaging.

Measuring the diameter of a hole is one of the most common measuring tasks in a production environment. And given the kind and number of tolerances for diameters, there are many different gaging techniques available to do these checks.